Conventionally, image forming apparatuses of an electrophotographic type, such as copying machines, printers, and facsimiles have been known. The image forming apparatus operates to form an electrostatic latent image on a surface of a photoreceptor and develop the electrostatic latent image with toner. The resulting toner image is transferred and fixed on a printing medium such as a sheet of paper. The toner used for the development of the electrostatic latent image is supplied to the photoreceptor surface from a developing unit. The toner in the developing unit is supplied from a toner bottle via a toner replenishing device and an eject pipe. That is, the toner is transported through a toner transport path, from the toner bottle to the developing unit.
A remaining toner on a photoreceptor drum also needs to be transported.
As methods of transporting toner, techniques using coil springs are disclosed in Patent Publication 1 (Japanese Laid-Open Patent Publication No. 40487/1992 (published on Feb. 10, 1992)), Patent Publication 2 (Japanese Laid-Open Patent Publication No. 2005-283631 (published on Oct. 13, 2005)), and Patent Publication 3 (Japanese Laid-Open Patent Publication No. 44172/1996 (published on Feb. 16, 1996)). Use of coil springs requires driving means, such as a motor, for rotating the coil springs.
In the techniques described in Patent Publications 2 and 3, a rotational axis member is provided in the entire space (hollow space) inside the coil spring, and the coil spring is rotated by the rotation of the rotational axis member. In Patent Publication 1, a rotational axis member is provided inside the coil spring, a predetermined distance away from an end of the coil spring.
In an arrangement where the toner bottle is disposed above the developing unit, the toner bottle and the developing unit are generally disposed in this order from above, with the toner replenishing device and the eject pipe placed in between, as shown in FIG. 18. In such case, a layout of these members looks like a square with an open side, as shown in FIG. 18, taking into consideration the layout of other components in the image forming apparatus. Here, a toner inlet leading from the toner bottle, and a toner outlet leading to the eject pipe are formed on one end of the toner replenishing device. A motor for rotating a coil spring is also disposed on this side of the device, in the case where the toner replenishing device uses a coil spring.
FIG. 19 shows an exemplary structure of a toner replenishing device in which the toner inlet, the toner outlet, and the motor are disposed on the same end of the device. FIG. 19 is an upper view of a toner replenishing device 1000.
As shown in FIG. 19, the toner replenishing device 1000 includes a cabinet 1001, two coil springs 1002 and 1003, rotational axis members 1004 and 1005 for supporting and rotating the coil springs 1002 and 1003, respectively, and a motor.
The cabinet 1001 is narrow and rectangular in shape, and an upper surface of the cabinet 1001 is detachable to store the coil springs 1002 and 1003 therein. In FIG. 19, the upper surface of the cabinet 1001 is not shown. At one end in the lengthwise direction of the cabinet 1001, the upper surface and bottom surface of the cabinet 1001 are respectively provided with a toner inlet 1006 leading from the toner bottle, and a toner outlet 1007 leading to the eject pipe.
The cabinet 1001 has a partition 1008 that extends along a lengthwise direction. The partition 1008 divides the cabinet 1001 into coil spring storing spaces 1009 and 1010 for respectively storing the coil springs 1002 and 1003. The coil spring storing space 1009 is sized so that the coil spring 1002 can be stored and rotated therein. The same is the case for the coil spring storing space 1010. The coil springs 1002 and 1003 are disposed in the coil spring storing spaces 1009 and 1010, respectively.
On the opposite end of the toner inlet 1006 and the toner outlet 1007 in the lengthwise direction of the cabinet 1001, the partition 1008 is provided with a bypass portion 1011 through which the coil spring storing spaces 1009 and 1010 communicate with each other.
With this structure, the toner that has flown into the coil spring storing space 1010 through the toner inlet 1006 moves to the bypass portion 1011 (in a direction of arrow G in FIG. 19) by the rotation of the coil spring 1003. Through the bypass portion 1011, the toner is transported to the coil spring storing space 1009. By the rotation of the coil spring 1002, the toner is transported to the toner outlet 1007 (in a direction of arrow H in FIG. 19). In this manner, the toner is agitated as it moves along the coil spring storing spaces 1009 and 1010, and is uniformly ejected to the developing unit.
When a rotational axis member is used to transmit the rotational force of the motor to the coil spring 1003, the rotational axis member has conventionally been mounted at an end of the coil spring 1003 on the side closer to the motor. However, as described above, the motor for rotating the coil spring 1003 is disposed at an end where the toner inlet 1006 is provided, as shown in FIG. 19. As a result, the rotational axis member occupies inside the coil spring 1003, directly below the toner inlet 1006.
FIG. 20(a) is a longitudinal section at end portions of the coil spring 1003 and the rotational axis member 1005, taken along a plane parallel to the rotational axis. FIG. 20(b) is a cross section of the coil spring 1003 and the rotational axis member 1005, taken along a plane perpendicular to the rotational axis. As shown in FIGS. 20(a) and 20(b), the rotational axis member 1005 occupies the space (hollow space) inside the coil spring 1003. Because the rotational axis member 1005 resides directly below the toner inlet, the toner from the toner bottle is not supplied smoothly.
One way to create more space below the toner inlet 1006 is to provide a transmitting member of the motor rotational force only at a terminus of the coil spring 1003. However, this is disadvantageous in terms of manufacture, because it requires welding or other processes to firmly join the transmitting member and the coil spring. Another drawback is that the force of the motor concentrates on the terminus of the coil spring and causes a fatigue in this portion of the coil spring, with the result that the coil spring is easily broken. Further, there is a problem of material recycling. That is, it requires labor to separately collect the coil spring, made of metal, and the transmitting member, made of resin, when the device is scrapped for disposal.